My chickens also love kale, and it's super easy to grow in the garden, stays green and tasty through many frosts in the fall, way past Thanksgiving even here in Colorado. So sad when it was finally frozen and dead, then I discovered that my local Vitamin Cottage had big boxes of produce "prep"stuff: slightly wilted greens, kale, etc that they would otherwise throw away, and my chickens love it! I love Vitamin Cottage because they only sell organic produce, but I've heard that almost all groceries will provide similar stuff that they would otherwise send to the landfill, and your chickens will be so pleased to take it off their hands. Check it out!